The soil microbe Bacillus thuringiensis (B.t.) is a Gram-positive, spore-forming bacterium characterized by parasporal crystalline protein inclusions. These often appear microscopically as distinctively shaped crystals. The proteins can be highly toxic to pests and specific in their activity. Certain B.t. toxin genes have been isolated and sequenced, and recombinant DNA-based B.t. products produced and approved. In addition, with the use of genetic engineering techniques, new approaches for delivering B.t. endotoxins to agricultural environments are under development, including the use of plants genetically engineered with endotoxin genes for insect resistance and the use of stabilized intact microbial cells as B.t. endotoxin delivery vehicles (Gaertner, F. H., L. Kim [1988 ] TIBTECH 6:S4-S7). Thus, isolated B.t. endotoxin genes are becoming commercially valuable.
Over the past 30 years, commercial use of B.t. pesticides has been largely restricted to a narrow range of lepidopteran (caterpillar) pests. Preparations of the spores and crystals of B. thuringiensis subsp. kurstaki have been used for many years as commercial insecticides for lepidopteran pests. For example, B. thuringiensis var. kurstaki HD-1 produces a crystal called a delta endotoxin which is toxic to the larvae of a number of lepidopteran insects.
In recent years, however, investigators have discovered B.t. pesticides with specificities for a much broader range of pests. For example, other species of B.t., namely israelensis and san diego (a.k.a. B.t. tenebrionis, a.k.a. M-7), have been used commercially to control insects of the orders Diptera and Coleoptera, respectively (Gaertner, F. H. [1989] "Cellular Delivery Systems for Insecticidal Proteins: Living and Non-Living Microorganisms," in Controlled Delivery of Crop Protection Agents, R. M. Wilkins, ed., Taylor and Francis, New York and London, 1990, pp. 245-255). See also Couch, T. L. (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-76; Beegle, C. C., (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. Krieg, A., A. M. Huger, G. A. Langenbruch, W. Schnetter (1983) Z. ang. Ent. 96:500-508, describe a B.t. isolate named Bacillus thuringiensis var. tenebrionis, which is reportedly active against two beetles in the order Coleoptera. These are the Colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni.
Recently, new subspecies of B.t. have been identified, and genes responsible for active .delta.-endotoxin proteins have been isolated (Hofte, H., H. R. Whiteley [1989] Microbiological Reviews 52(2):242-255). Hofte and Whiteley classified B.t. crystal protein genes into 4 major classes. The classes were CryI (Lepidoptera-specific), CrylI (Lepidoptera- and Diptera-specific), CrylII (Coleoptera-specific), and CryIV (Diptera-specific). The discovery of strains specifically toxic to other pests has been reported. (Feitelson, J. S., J. Payne, L. Kim [1992] Bio/Technology 10:271-275).
The cloning and expression of a B.t. crystal protein gene in Escherichia coli has been described in the published literature (Schnepf, H. E., H. R. Whitely [1981] Proc. Natl. Acad. Sci. USA 78:2893-2897). U.S. Pat. No. 4,448,885 and U.S. Pat. No. 4,467,036 both disclose the expression of B.t. crystal protein in E. coli. U.S. Pat. Nos. 4,797,276 and 4,853,331 disclose B. thuringiensis strain san diego (a.k.a.B.t. tenebrionis, a.k.a. M-7) which can be used to control coleopteran pests in various environments. U.S. Pat. No. 5,151,363 discloses certain isolates of B.t. which have activity against nematodes. Many other patents have issued for new B.t. isolates and new uses of B.t. isolates. The discovery of new B.t. isolates and new uses of known B.t. isolates remains an empirical, unpredictable art.
Insects in the family Scarabaeidae (scarabs) constitute a serious pest control problem, especially when destructive larval stage insects infest high value turf found in golf courses, playing fields and lawns. The larvae of many species also attack grains, tuberous crops, and ornamentals. Larvae are called "white grubs" or "chafer grubs" and can be found in decaying organic matter (rotting leaves, manure, etc.) or 2-10 cm. deep in soil where they consume the plant roots. In turf infested areas there can be as many as 30 grubs per square foot. The damage caused by an infestation becomes most apparent in the fall when the third instar grubs are feeding. Adult beetles of some scarab species will feed on a wide variety of vegetative host, damaging foliage, fruit and flowers of woody and herbaceous plants. In the U.S. and Europe, populations of larvae and adults have developed resistance to chemical insecticides such as the organochlorines and DDT.
Several scarab pests are of economic importance. Particularly important pests in the U.S., especially east of the Rockies, but also in the Western States, are the masked chafers, Cyclocephala sp. In the east, the northern masked chafer, C. borealis, and the southern masked chafer, C. immaculata, are common pests, while, in California, C. hirta and C. pasadenae are present. Also, in the U.S., especially in the area east of the rockies, infestations of Japanese beetles Popillia sp., May or June beetles Phyllophaga sp., black turfgrass beetles Ataenius sp., European chafers Rhizotrogus sp., tend to necessitate the greatest amount of insecticide treatments. Other important scarab pests in the U.S. can be quite damaging but localized such as with Oriental beetles Anomala sp., hoplia chafers Hoplia sp., green June beetle Cotinis sp., and Asiatic garden beetles Maladera sp. Several scarabs not present in the U.S. are of economic importance in Europe, including rose chafers Cetonia sp., cockchafers Melolontha sp., flower beetles Adoretus sp., and garden chafers Phyllopertha sp. The green June beetles, Cotinis sp., can cause serious damage where populations become abundant. The adults are attracted to ripenine fruit and will devour figs, peaches and other thin skinned fruit while on the tree. Larvae are attracted to decaying organic matter and most commonly become pests in turf or fields which have been fertilized with manure. The feeding and tunnelling of the large larvae can become disruptive. The eastern green June beetle Cotinis nitida is present in the mid-western and eastern states, while the green June beetle C. mutabilis occurs in many of the western states.